Like United Launch Alliance’s proposed Vulcan rocket recovery system, Airbus is focusing on bringing the boosters’ most expensive part—the engines—back to Earth. Enclosed in a pod, Airbus’ engines would autonomously land themselves on a runway. ULA envisions using a helicopter to snag its parachuting engines from the air.

The firms have sparred over a contract to take over one of NASA’s mothballed shuttle launch pads (SpaceX won) and a patent for landing a rocket on an ocean barge (ongoing), but they seem to agree that returning their rockets' first-stage boosters intact is a better way to go, at least initially.

Blue Origin is partnering with ULA on the development of new rocket engine, the BE-4. ULA plans to integrate the BE-4 into a landing system called SMART, an acronym for Sensible, Modular, Autonomous Return Technology. The idea is that after first-stage separation, the engine compartment detaches from the booster, deploys an inflatable heat shield and re-enters the atmosphere. Parachutes open to slow the module’s descent, setting the stage for a mid-air capture by helicopter and return to Earth.

Airbus’ system, called Adeline (the ADvanced Expendable Launcher with Innovate engine Economy) likewise focuses on rocket engine recovery, rather than whole boosters. Airbus envisions returning the engines and the launcher’s avionics equipment in a re-entry module, which potentially can be adapted to any launcher.

“The concept could be implemented on the Ariane 6 launcher, for which the current development integrates the ‘reusability’ element. Adeline could even be ‘grafted’ onto any launcher, however large or small,” Airbus said in a statement.

The return module would be positioned at the base of the launcher. After detaching from the rocket’s upper stages, the module, protected by a heat shield, would re-enter the atmosphere, then fly and land itself on a runway similar to an unmanned aircraft.

For atmospheric flight, the module would use winglets and a set of deployable propellers.

“Adeline requires no additional ground infrastructure for its return to Earth. A normal runway is adequate,” Airbus said.

What is required for both ULA’s SMART and Airbus’ Adeline is time. ULA’s Vulcan rocket won’t be ready for a test flight until around 2019 and demonstrating a recoverable rocket engine won’t come until later. Airbus said a debut flight of Adeline is scheduled for 2025.

Engineers and accountants can debate the technical and financial tradeoffs of recovering engines versus boosters, but in the end the discussion may be moot.

After a series of close calls, SpaceX is gearing up for another attempt next week to land a Falcon 9 rocket on a specially outfitted drone ship stationed in the Atlantic Ocean, northeast of its Cape Canaveral, Florida, launch pad.

The Falcon 9 is slated to lift off at 10:21 EDT on Sunday and deliver a Dragon cargo ship to the International Space Station for NASA. Once the rocket’s first-stage separates from the upper-stage and capsule, it will flip around and fire braking burns to attempt to land itself on what SpaceX calls “an autonomous spaceport drone ship.”

The landing has been attempted twice previously. The first time, the rocket ran out of hydraulic fluid, which was needed to control its steering fins. The booster crashed into the barge and exploded.

The next time, the 14-story first-stage touched down, but with too much lateral motion. It tipped over and exploded. Engineers later determined an engine throttle valve didn’t respond fast enough.

SpaceX already has gotten its boosters to make practice touchdowns, hovering just above the ocean’s surface, before toppling over.

The company is confident of eventual success and is preparing landing pads on the ground, near its Florida and California launch sites.

Blue Origin, which plans to use the BE-4 in its own orbital launch system, appears to be following a similar path.

The company’s suborbital New Shepard launcher, which made its debut test flight in April, dispatched a dummy capsule for a successful parachute return to Earth. The rocket then attempted to fly itself back to a landing pad near Blue Origin’s west Texas launch site, but the booster's hydraulic system lost pressure, dooming the landing attempt.